Rectifier



r Patented Feb. 7,

UNl'lED STATES PATENT OFFlCE Carl 0. Hein, rorifnna, 1a., asslgnor toWestinghouse Electric Corporation, East Pittsburgh, Pa., a corporationof Pennsylvania No Drawing.

Claims. 1

Application camber- 19,1945, Serial n0.- 623,453

' My invention relates to copper oxide rectiflers and. in particularrelates to methods of forming a contact layer for the oxidized surface.

Copper oxide rectifiers made in accordance with United States Patent1,640,335, Grondahl, in which an oxidized surface forming on a copperplate is provided with a counter-electrode capable of conducting currentinto the oxide have come into wide use in recent years.

In accordance with the abovementioned Grondahl patent thecounter-electrode was formed by first coating the oxide surface withgraphite and then covering it with a thin plate of lead or otherimpressionable material. A considerable improvement in the method ofapplying the counter-electrode has been made in recent years through thereplacement of the above named described graphite and lead washercounter-electrode by one produced by reducing a portion of the oxidesurfaces to metallic copper. For many purposes ithas been founddesirable that the reduced copper surface should be provided with aprotective plating of nickel applied by deposition from an electrolyticplating bath. However, it has been found that there is a tendency tocrack in some deposits of the nickel coating and difficulty frequentlyhas been found in the fact that the plating solution apparentlypenetrates minute cracks or interfaces between crystals on the oxidizedcopper surface with resulting deposits of nickel therein. The nickelthus formed in the cracks sometimes is penetrative enough to actuallyform a bridge or short circuit between the reduced copper on the outsideof the copper oxide layer and the mother copper on the inner sidethereof. Thus in quantity production it was found that a substantialpercentage of the rectifiers subjected to the above mentionedelectrolytic process are short circuited and rendered worthless.

It has also been found necessary, where the above mentioned electricalprocess is used in producing the counter-electrode, to burnish the outersurface of the electrolytic deposition if a low resistance of therectifier to current flow is to be obtained in its conductive direction.Such a burnishing operation is an additional expense of by no means anegligible amount in rectifier manufacturing.

I have investigated the structure of the electrolytically treatedsurface of such rectifiers and have discovered that the reduction of theoxide at'various points on the surface appears to be uneven, beinglargely concentrated on the lines of crystalline division of the oxidesurface.

Though reduction occurs almost everywhere at the crystal boundaries itleaves the major portion of the crystal surfaces in its originaloxidized condition. This is particularly true during the earlier stagesof the reduction, later stages usually resulting in a reduction of allportions of the oxide surface; but the reduction is still most completealong the crystal boundaries. When such surfaces are introduced into theelectrolytic plating bath, the nickel deposits largely along the crystalboundaries, penetrating the cracks between crystals and at times shortcircuiting the oxide crystals themselves as already described.

In accordance with my present invention I have discovered that if theoxide surface is lightly abraded prior to the step of reducing it tocopper most of the effects of non-uniformity in reduction is avoided. Inparticular the selective reduction in the crystal boundaries is greatlyreduced. Reduction appears in fact to tend to occur principally alongthe furrows made by the abrading material; hence by being certain thatabrasion covers substantially the entire surface of the oxide layer, aneifective uniformly distributed reduction can be effected. Subsequentdeposition of the nickel by electroplating follows the reduced copper inthese furrows and very little penetration of depositing nickel into theboundaries between crystals occurs.

One object of my invention accordingly is to provide an improved form ofcopper oxide rectifler.

. Another object of my invention is to provide an improved form ofcounter-electrode for copper oxide rectifiers.

Still another object of my invention is to provide an improved method ofproducing electrical .contacts for copper oxide surfaces.

Still another object of my invention is to provide a method forproducing counter-electrodes for copper oxide rectifiers.

Other objects of my invention will; become apparent upon reading thefollowing description:

Rectifiers in accordance with my invention may be made by firstoxidizing clean copper plates or discs by heating them in an oxygenatmosphere at a temperature not far below the melting point of copper.The plates may then be subjected to heat treatment such as is describedin the application of Charles S. Duncan, Serial No.'625,452, filed Oct.29, 1945, now Patent No. 2,459,630, issued January 18, 1949, assigned tothe assignee of this application. After the cupric oxide formed on theouter surface of the units has been removed by pickling in acidsolusteel. A current density of 80 milliamperes per square inch at 50 to60 volts direct current may be applied for two and one half to threeminutes.

The units are then removed from the bath,

thoroughly rinsed in distilled water and then put into an electrolyticplating bath comprising nickel sulphate at 200 grams to the liter andboric acid 30 grams to the liter. The units should constitute thecathode of this electrolytic bath which ma subject them to a currentdensity of 100 milliamperes per square inch for about three and one halfminutes. The units may be removed then from the plating bath, rinsedthoroughly in both hot and cold water and dried.

Investigation has shown that rectifiers produced as above described havea lower resistance to current flow in their conductive direction thanrectiiiers produced by the prior art processes. Furthermore, a sumeientreduction of the oxide layer to provide acceptable electrical contactcan be produced in about one-half minute as against a treatment ofsomething like three minutes by the prior art methods. This reduction inthe time required for the electrolytic treatment is of course extremelyimportant in quantity production of copper oxide rectifiers.

I claim as my invention:

1. The method of providing contact surfaces for copper oxide rectiflerswhich comprises forming a uniform coating of cuprous oxide on therectifier, subjecting the surface of the cuprous oxide to abrasion, andsubjecting the abraded surface to chemical reduction.

2. The method of providing contact surfaces for copper oxide rectifierswhich comprises forming a uniform coating of cuprous oxide on therectifier, subjecting the surface of the cuprous oxide to abrasion, andsubjecting the abraded surface to chemical reduction and electroplatingthe surface resulting from such reduction.

3. The method of providing contact surfaces for copperoxide rectifierswhich comprises forming a uniform coating of cuprous oxide on therectifier, subjecting the surface of the cuprous oxide to abrasion, andsubjecting the surface of the cuprous oxide to an electrolytic bath.

4. The method of providing contact surfaces for copper oxide rectifierswhich comprises forming a uniform coating of cuprous oxide on therectifier, subjecting the surface of the cuprous oxide to abrasion, andsubjecting the surface of the cuprous oxide to an electrolytic bath, and

electroplating the surface produced by such treatment.

5. The method of providing electrical contacts for metallic oxidesurfaces which comprises abrading said surfaces, subjecting them to achemical reducing action.

6. The method of providing electrical contacts for metallic oxidesurfaces which comprises abrading said surfaces and subjecting themthereafter to an electro-chemical reducing action.

7. The method of providing electrical contacts for metals having surfacelayers consisting of compounds of said metals which comprises abradingsaid surfaces, and subjecting them thereafter to an electro-chemicalaction.

8. The method of providing electrical contacts for metallic oxidesurfaces which comprises abrading said surfaces, subjecting themthereafter to an electro-chemical reducing action and electroplatingthem thereafter.

9. A copper oxide rectifier comprising mother copper having an oxidizedsurface, said surface being traversed by abrasion marks which have beensubjected to electrolytic reduction.

10. A copper oxide rectifier comprising mother copper having an oxidizedsurface, said surface being traversed by abrasion marks which have beensubjected to electrolytic reduction and subsequently electro-plated withmetal.

CARL C. HEIN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,892,832 Geiger Jan. 3, 19331,926,132 .Ackerly Sept. 12, 1933 2,239,770 Becker Apr. 29, 19412,383,311 Hein Aug. 21, 1945

1. THE METHOD OF PROVIDING CONTACT SURFACES FOR COPPER OXIDE RECTIFIERSWHICH COMPRISES FORMING A UNIFORM COATING OF CUPROUS OXIDE ON THERECTIFIER, SUBJECTING THE SURFACE OF THE CUPROUS OXIDE TO ABRASION, ANDSUBJECTING THE ABRADED SURFACE TO CHEMICAL REDUCTION.